/Engine/Source/Runtime/AIModule/Classes/BehaviorTree/BlackboardComponent.h
Register observer for blackboard key
[FDelegateHandle](API\Runtime\Core\Delegates\FDelegateHandle) RegisterObserver ( [FBlackboard::FKey](API\Runtime\AIModule\BehaviorTree\Blackboard\FKey) KeyID, const [UObject](API\Runtime\CoreUObject\UObject\UObject) * NotifyOwner, FOnBlackboardChangeNotification ObserverDelegate )